[build] Update gn to match Fuchsia

Bug: fxbug.dev/56683
Change-Id: I1442dde1cb4ac834b55e7460f5c3533ccf097be1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/155306
Auto-Submit: Roland McGrath <[email protected]>
Reviewed-by: Ryan Macnak <[email protected]>

Author: frobtech

DEPS

@@ -54,10 +54,10 @@ vars = {
   # As Flutter does, we use Fuchsia's GN and Clang toolchain. These revision
   # should be kept up to date with the revisions pulled by the Flutter engine.
   # The list of revisions for these tools comes from Fuchsia, here:
-  # https://fuchsia.googlesource.com/buildtools/+/master/fuchsia.ensure
+  # https://fuchsia.googlesource.com/integration/+/HEAD/prebuilts
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
   "clang_revision": "7e9747b50bcb1be28d4a3236571e8050835497a6",
-  "gn_revision": "239533d2d91a04b3317ca9101cf7189f4e651e4d",
+  "gn_revision": "1e3fd10c5df6b704fc764ee388149e4f32862823",
 
   # Scripts that make 'git cl format' work.
   "clang_format_scripts_rev": "c09c8deeac31f05bd801995c475e7c8070f9ecda",